Systems and methods for current and voltage monitoring

ABSTRACT

A cable for monitoring current and voltage includes a plug, a socket, first and second conductors extending from the plug to the socket, a current and voltage monitoring module, a transceiver, and a housing. The current and voltage monitoring module is coupled to the first and second conductors, and is configured to measure current and voltage usage levels of the conductors. The transceiver is coupled to the current and voltage monitoring module and is configured to receive data related to the current and voltage levels and transmit the data related to the current and voltage levels. The housing is configured to house the current and voltage monitoring module, the transceiver and one of the socket and the plug.

RELATED APPLICATIONS

This application is a divisional of pending U.S. patent application Ser.No. 13/194,484, filed Jul. 29, 2011, entitled SYSTEMS AND METHODS FORCURRENT AND VOLTAGE MONITORING, which is incorporated herein byreference in its entirety.

BACKGROUND

Datacenters often include multiple power distribution units (PDU's)contained within equipment racks. Intelligent rack-mounted powerdistribution units, sometimes referred to as “rack PDU's,” provide powerfor multiple computing devices such as servers contained with theequipment racks. The computing devices typically use large amounts ofenergy. It is useful to measure the current and voltage used by each ofthe computing devices and other associated equipment such as coolingunits to determine the overall efficiency of the datacenter. Current atan electrical outlet can be measured using wall plug-mounted devices orelectrical power strips, but these units can become impractical in PDU'shaving multiple outlets.

SUMMARY

Systems and methods for current and voltage monitoring inside thehousing of a cable socket or plug are provided. According to one aspect,systems and methods for monitoring current and voltage usage by eachcomputing device in a rack are provided.

According to one aspect, a cable for monitoring current and voltageincludes a plug, a socket, first and second conductors extending fromthe plug to the socket, a current and voltage monitoring module, atransceiver, and a housing. The current and voltage monitoring module iscoupled to the first and second conductors, and is configured to measurecurrent and voltage usage levels of the conductors. The transceiver iscoupled to the current and voltage monitoring module and is configuredto receive data related to the current and voltage levels and transmitthe data related to the current and voltage levels. The housing isconfigured to house the current and voltage monitoring module, thetransceiver and one of the socket and the plug.

According to one embodiment, the transceiver is configured to use awireless low power communication protocol to transmit the data relatedto the current and voltage levels. In one example, the wireless lowpower communication protocol is IEEE standard 802.15.4.

According to another embodiment, the current and voltage monitoringmodule is configured to operate in one of a sleep mode and a wake mode.The wake mode may have the transceiver energized for either none or partof the wake time. In another embodiment, the cable includes a capacitorconfigured to store operating power for at least one of the current andvoltage monitoring module and the transceiver. According to a furtherembodiment, the current and voltage monitoring module is configured tocharge the capacitor in a sleep mode of operation.

In one embodiment, the socket is a IEC C13 standard socket. In anotherembodiment, the plug is a IEC C14 standard plug. In a furtherembodiment, the cable is a three phase power cable.

According to another aspect, a method for monitoring current and voltageof devices mounted in an equipment rack, includes installing multiplecables in the equipment rack, each of the cables having a current andvoltage monitoring module, coupling each of the cables to a computingdevice in the equipment rack, sending current and voltage data from atransceiver in each of the cables to a server, and monitoring, at theserver, the current and voltage data from each of the cables.

According to one embodiment, the method also includes receiving, at awireless receiver, the current and voltage data, and transmitting thecurrent and voltage data to the server. According to another embodiment,sending voltage and current data includes sending current and voltagedata at intermittent intervals. According to one feature, each of thecables sends current and voltage data at different, non-overlapping timeintervals.

According to another embodiment, the method also includes intermittentlydrawing power from a capacitor in the cable for sending current andvoltage usage information from the transceiver. In a further embodiment,the method includes intermittently drawing power from the capacitor forpowering a current sensor.

In another embodiment, installing multiple power cables includesinstalling power cables having the current and voltage monitoring moduleand the transceiver contained in a housing configured to house at leastone of a socket end and a plug end of each cable.

According to another aspect, a system is provided that includes anequipment rack having mounting rails for devices to be installed in therack, multiple computing units mounted on the mounting rails, multiplepower cables having current and voltage monitoring circuitry, and aserver configured to receive current and voltage data from each of thecables. Each cable is coupled to one of the computing units, and eachcable includes a transceiver for sending current and voltage data.

According to one embodiment, the system includes a wireless receiver forreceiving the current and voltage data from the transceiver andtransmitting the current and voltage data to the server. According toanother embodiment, the wireless receiver is configured, in a firstmode, to accept transceivers into a network controlled by the wirelessreceiver and the wireless receiver is configured, in a second mode, toprevent new transceivers from connecting to the network controlled bythe wireless receiver. According to one embodiment, the wirelessreceiver is configured to communicate using a wireless low powercommunication protocol.

BRIEF DESCRIPTION OF THE FIGURES

The accompanying drawings are not intended to be drawn to scale. In thedrawings, each identical or nearly identical component that isillustrated in various figures is represented by a like numeral. Forpurposes of clarity, not every component may be labeled in everydrawing. In the drawings:

FIG. 1 is a diagram of the back of a rack of servers in accordance withone embodiment of the invention;

FIG. 2 is a diagram of a plug, cable and socket in accordance with oneembodiment of the invention;

FIG. 3A is a front perspective view of a cable socket showing currentand voltage monitoring circuitry in accordance with an embodiment of theinvention;

FIG. 3B is a back perspective view of a cable socket showing current andvoltage monitoring circuitry in accordance with an embodiment of theinvention;

FIG. 4 is a schematic diagram of current and voltage monitoringcircuitry in accordance with an embodiment of the invention;

FIG. 5 is a chart showing an exemplary sleep-wake cycle of an integratedcircuit and transceiver in accordance with an embodiment of theinvention;

FIG. 6 is a schematic diagram of a system for monitoring the current andvoltage usage of multiple devices in accordance with an embodiment ofthe invention; and

FIG. 7 is a flow chart of a method of monitoring the current and voltageusage of multiple devices in accordance with an embodiment of theinvention.

DETAILED DESCRIPTION

Embodiments of this invention are not limited in their application tothe details of construction and the arrangement of components set forthin the following description or illustrated in the drawings. Embodimentsof the invention are capable of other embodiments and of being practicedor of being carried out in various ways. Also, the phraseology andterminology used herein is for the purpose of description and should notbe regarded as limiting. The use of “including,” “comprising,” or“having,” “containing,” “involving,” and variations thereof herein, ismeant to encompass the items listed thereafter and equivalents thereofas well as additional items.

FIG. 1 is a diagram 100 of the back side of an equipment rack 102containing computing devices 104 a-104 j according to an embodiment ofthe invention. The back side of the rack 102 includes two rack-mountedPDU's 103 a and 103 b each having multiple outlet receptacles 106 a-106j and 108 a-108 j. The computing devices 104 a-104 j are plugged intothe outlet receptacles 106 a-106 j and 108 a-108 j with cables 110 a-110j and 112 a-112 j. The computing devices 104 a-104 j are each plugged into two outlet receptacles, one outlet receptacle of PDU 103 a and oneoutlet receptacle of 103 b. In some embodiments, the PDU's are poweredfrom different sources of power to provide redundant power to thecomputing devices.

According to one feature, the cables 110 a-110 j and 112 a-112 j includecurrent and voltage monitoring technology which monitors the current andvoltage usage through each cable 110 a-110 j and 112 a-112 j.Additionally, the cables 110 a-110 j and 112 a-112 j each include atransceiver which transmits the current and voltage usage measurementsfrom the cable to a wireless receiver. In one example, the wirelessreceiver 114 is a USB dongle, and the USB dongle is plugged into one ofthe computing devices 104 a-104 j. In FIG. 1, the wireless receiver 114is plugged into the computing device 104 b. The computing device 104 breceives the current and voltage usage measurements from the wirelessreceiver 114.

According to one embodiment, a user can view the current and voltageusage measurements using the computing device 104 b. The measurementsmay be used to monitor the current and voltage usage of the computingdevices 104 a-104 j on the rack 102. In one example, a user may use themeasurements to determine if one of the computing devices 104 a-104 j isusing an unusually large amount of power. According to one feature, themeasurements allow a user to monitor the power usage of each computingdevice 104 a-104 j on a rack, and compare the power usage of eachcomputing device 104 a-104 j with the power usage of the other devices104 a-104 j. A user may also compare power usage of computing devices onmultiple racks. In one example, the computing devices 104 a-104 j areservers.

Although the illustrative rack PDU 102 includes ten computing devices,in other embodiments, the rack PDU 102 may include any selected numberof computer devices. Similarly, although the illustrative rack PDU 102includes ten electrical outlets 106 a-106 j on one side and tenelectrical outlets 108 a-108 j on the other side, and two rack PDU's 103a and 103 b, in other embodiments, the rack PDU 102 may include anyselected number of electrical outlets on each side, and may include moreor less rack PDU's. In one example, the rack PDU's 103 a, 103 b includes20 electrical outlets each. In another example, the rack PDU's 103 a and103 b include 25 electrical outlets each.

According to one feature, the wireless receiver 114 that receives thecurrent and voltage measurements from the cables is a USB dongle thatincludes a transceiver that uses a low power, wireless communicationstandard. In one example, the wireless receiver 114 is a USB dongle witha transceiver that uses a IEEE standard 802.15.4 communication standard.In another example, the wireless receiver 114 is a USB dongle thatincludes a Zigbee® transceiver. The USB dongle is a peripheral adapterthat provides short-range low-power wireless connectivity betweenwireless transceivers. In one example, the USB dongle is a Digi XStick®.In another example, the wireless communication protocol is Bluetooth. Inother examples, the wireless communication protocol may be a similarsimple low-power short-range protocol.

According to another embodiment, the wireless receiver 114 is aself-contained unit and is plugged into an outlet receptacle andincludes a wired or wireless Ethernet connector and a processor. Thewireless receiver 114 is configured to wirelessly receive data frommultiple current and voltage monitoring cables. According to onefeature, the wireless receiver 114 transmits the data to a computer or anetwork through a TTL serial interface. In one example, the wirelessreceiver 114 transmits the data to a Radiocrafts module. According toone feature, when the wireless receiver 114 is plugged into an outletreceptacle, it covers only the one outlet receptacle that it is pluggedinto and does not obstruct adjacent outlet receptacles.

In one embodiment, the wireless receiver 114 includes one or more rotaryswitches. The rotary switches may support a selected number of networkedtransceivers. For example, all the devices in one network may share aPersonal Area Network IDentification (PANID) number, and a device mayreceive traffic only from other devices having the same PANID number.PANID numbers are described in further detail in U.S. patent applicationSer. No. 12/976,352 filed Dec. 22, 2010 and titled “WirelessCommunication System and Method,” assigned to American Power ConversionCorporation, the entirety of which is hereby incorporated by itsentirety herein. In one example, the rotary switches support up to about100 networks. In one embodiment, the wireless receiver 114 includes anLED light, which may be used to indicate whether the wireless receiveris currently accepting new child transceivers to its network. In anotherembodiment, the wireless transceiver 114 includes a push button, which auser may push to cause the receiver to attempt to reconnect with a childtransceiver.

According to one embodiment, pushing and holding a button on thewireless receiver 114 will clear its child transceiver list and causethe wireless receiver 114 to be open to accepting new child transceiversto its network. According to one feature, an LED on the wirelessreceiver 114 will turn on solid green while it is open to accepting newchild transceivers. According to another feature, pressing the buttonagain while the LED is green will put the wireless receiver 114 backinto no-join mode, in which it will not accept new child transceivers toits network.

According to another embodiment, a wireless receiver 114 may receivesignals from power monitoring devices contained in the power cables forall the devices in a rack PDU. In one embodiment, a standard rack PDUincludes 40 unit spaces. In one example, each device on the rack PDUoccupies two unit spaces, so a standard rack PDU may contain 20 devices.Each device accepts two input cables, so there are 40 input cables, eachhaving a power monitoring device with a transceiver transmitting currentand voltage measurements to the wireless receiver 114. In anotherembodiment, a tall rack PDU includes 48 unit spaces. In one example, atall rack PDU includes 24 devices each accepting two input cables. Thus,the tall rack PDU wireless receiver 114 receives signals from 48 cables.According to one feature, the transceiver in each cable transmits dataat regular intervals, and the intervals are spaced such that differenttransceivers transmit data at different times. According to one feature,this conserves the receiving bandwidth of the receiver 114.

FIG. 2 is an illustration of a cable 200 including a plug 202, a cord204 and a socket 206, according to an embodiment of the invention. Thecable includes current and voltage monitoring circuitry and atransceiver. In one embodiment, the current and voltage monitoringcircuitry and the transceiver are enclosed in the housing of the socket206. In another embodiment, the current and voltage monitoring circuitryand the transceiver are enclosed in the housing of the plug 202. Thecurrent and voltage monitoring circuitry measures the current andvoltage draw from the socket 206. The current and voltage measurementsare sent to the transceiver and the transceiver wirelessly transmits themeasurements. According to one aspect, the plug 202 of the cable 200covers only one outlet receptacle of a typical rack PDU.

According to one embodiment, the socket 206 is a standard IEC C13 socketand the plug 202 is a standard IEC C14 plug. According to the IEC C13standard, the current rating of the socket is 15 A under a UL(Underwriters Laboratories Inc) or CSA (Canadian Standards Association)IEC C13 standard, and the current rating of the socket is 10 A under aVDE (Verband der Electrotechnik) or European IEC C13 standard. Thevoltage rating is 250 Volts. Under the IEC C13 standard, the two outerpinholes in the socket are spaced 14 mm apart. According to oneembodiment, the housing of the socket 206 may be slightly larger than atypical socket housing to accommodate the current and voltage monitoringcircuitry, but the socket 206 meets the IEC C13 standard.

According to other embodiment, the socket 206 may be another type ofsocket and the plug 203 may be another type of plug. In one example, thesocket 206 is a type of standard IEC 60320 socket and the plug 203 isanother type of standard IEC 60320 plug. In various examples, the socket206 may be an IEC C1, C3, C5, C7, C9, C11, C15, C15A, C17, C19, C21 orC23 socket. The plus 202 may be a corresponding IEC C2, C4, C6, C8, C10,C12, C16, C16A, C18, C20, C22 or C24 plug.

According to another embodiment, the socket 206 includes a Hall-effectsensor which acts like a push button. When a magnet is waved near theHall-effect sensor, the sensor acts to reset the transceiver and causeit to search for a wireless receiver. In one embodiment, a magnet may bebuilt into the wireless receiver 114, and the socket 206 may be held inclose proximity to the wireless receiver 114 to activate the Hall-effectsensor in the socket 206 and cause it to search for a wireless receiver.In another example, the wireless receiver 114 may be held in closeproximity to the socket 206 to activate the Hall-effect sensor.According to one advantage, including a magnet in the wireless receiver114 allows a user to easily locate a magnet to use to reset thetransceiver.

In another embodiment, the magnet used to activate the Hall-effectsensor is an external hand-held magnet. According to one embodiment,pushing the virtual button (or activating the Hall-effect sensor) causesthe wireless transceiver to exit a “no-join” mode and search for awireless receiver. When the wireless transceiver detects a wirelessreceiver, and the wireless receiver accepts the transceiver to itsnetwork, the transceiver returns to the no-join mode. According to onefeature, while the wireless transceiver is searching for a receiver, anLED light on the wireless receiver 114 lights up green. Once thewireless transceiver has found a receiver and joined a network, the LEDlight turns off as the transceiver returns to the no-join mode.

According to one embodiment, when the virtual button on the socket 206is activated, the transceiver will first attempt to join the network ofthe receiver to which it was most recently transmitting data. Accordingto one feature, the transceiver attempts to join its previous networkfirst, in case the virtual button was unintentionally pushed. Accordingto one embodiment, an existing child transceiver may attempt to join awireless receiver network even if the wireless receiver is in a no-joinmode and is not accepting new child transceivers if the childtransceiver is already on the wireless receiver's list of networkedchild transceivers. According to one embodiment, the wirelesstransceivers contain a network number algorithm for PANID (Personal AreaNetwork IDentifier) and an encryption key for accessing the wirelessreceiver. According to one feature, the wireless transceiver is onlyactive for a short period at a time, and only searches for a wirelessreceiver during its active period.

According to one embodiment, the current and voltage monitoringcircuitry measures the power usage through the socket 206 of the cable200. The measurements include root mean square (RMS) voltage, RMScurrent, RMS volt-amperes ((RMS volts)*amperes), and RMS Watts.According to one example, RMS Watts is the sum of multiple samples of(volts*amperes). For example, RMS Watts may be the sum of all thesamples of (volts*amperes) from one AC cycle. According to oneembodiment, the measurements may include distortion and crest factor.According to another embodiment, a processor in the wireless receivercalculates the power factor of a set of measurements, where the powerfactor is the ratio of volt-amperes to Watts. According to anotheraspect, the current and voltage monitoring circuitry is housed in theplug 202 of the cable 200 rather than in the socket 206.

According to one aspect, the firmware for the current and voltagemonitoring circuitry may be updated remotely through the wirelesscommunication link to the wireless receiver 114. In one example, serialdata for updating the firmware is transmitted to a digital Hall-effectsensor in the current and voltage monitoring circuitry.

According to another aspect, each cable 200 undergoes initial factorytesting before use, and the initial factory testing includes identifyinga MAC address and a manufacturing date for the cable 200. According toone feature, the MAC address and product serial number are included on alabel on the power cord. According to one feature, the factory testingincludes calibration of the current sensor's offset and gain. In oneexample, the current sensor may be calibrated wirelessly by transmittingbit stream data to the digital Hall effect sensor. According to onefeature, the digital Hall effect sensor has a bandwidth of about 100kHz.

FIG. 3A is a top perspective view of a socket portion 206 of the cable200 with a portion of the housing removed to show current and voltagemonitoring circuitry 302, according to an embodiment of the invention. Acurrent sensor 304 is positioned on the live line 306 of the powerconductors in the cable. A power supply capacitor 308 is positionedadjacent to the current and voltage monitoring circuitry 302. Thecurrent and voltage monitoring circuitry 302 includes a transceiver fortransmitting current and voltage measurements. According to one feature,the power supply capacitor 308 stores incoming power and then providesan extra charge to the transceiver at regular intervals, which thetransceiver may use to transmit the recorded current and voltagemeasurements at regular intervals.

According to one embodiment, the current sensor 304 detects electricalcurrent in the live line 306 and generates a signal proportional to thedetected current. In one example, the current sensor 304 is a compact,precision 55 amp current sensor, and it may be designed to operatebetween about 3V and about 5.5V. The current sensor 304 may have aradial format.

FIG. 3B is a side perspective view of the socket portion 206 of thecable 200 with a portion of the housing removed to show the current andvoltage monitoring circuitry 302, according to an embodiment of theinvention. The current sensor 304 is shown positioned around the liveline 306. The power supply capacitor 308 is positioned adjacent to thecurrent and voltage monitoring circuitry 302. The current and voltagemonitoring circuitry 302 is adjacent to the line 306.

FIG. 4 is a schematic diagram of current and voltage monitoringcircuitry 400 including a first integrated circuit 402 having atransceiver, according to an embodiment of the invention. The currentand voltage monitoring circuitry 400 also includes a current sensor 304,voltage monitoring circuitry including first 430, second 432, third 440,fourth 442 and fifth 444 resistors. Line 406 is the AC (alternatingcurrent) line, and current drawn on line 406 as well as voltage over theline 406 will be measured by the circuitry 400 and transmitted by thetransceiver in the integrated circuit 402.

According to one aspect, the power supply capacitor 308 is the mainpower supply capacitor. During the positive half of the AC cycle,current through the first diode 412 charges the power supply capacitor308. In one example, the power supply capacitor 308 has a capacitance of0.33 μF and is rated for 250 VAC. During the negative half of the ACcycle, the power supply capacitor 308 discharges power through a seconddiode 416 to a main storage capacitor 418. In one example, the mainstorage capacitor 418 has a capacitance of 47 μF and a voltage of 16V.Between the second diode 416 and the main storage capacitor 418 is afirst common node 426. According to one feature, the power supplycapacitor 308 charges the main storage capacitor 418. The third diode420 is a Zener diode and acts as a voltage regulator or a voltagelimiter, preventing overcharging of the main storage capacitor 418.

The first common node 426 is coupled to a second integrated circuit 422.According to one feature, the second integrated circuit 422 includes avoltage regulator, that in one embodiment provides an output voltage of3.3 Volts. According to one feature, the second integrated circuit 422is coupled to ferrite bead 428, which is used to prevent RFinterference.

According to one aspect, a series of resistors form a voltage dividerfrom which voltage may be monitored. A first resistor 430 is coupled inseries with a second resistor 432. Between the first resistor 430 andthe second resistor 432 is a second common node 434. The second commonnode 434 is connected to line 436. Line 436 connects the second commonnode 434 with the first integrated circuit 402. Between the neutral line438 and the second common node 434 are the third 440, fourth 442 andfifth 444 resistors, connected in series. According to one feature, thethird 440, fourth 442 and fifth 444 resistors provide a safetymechanism, such that if one of the third 440, fourth 442 and fifth 444resistors fails, the other two resistors will provide sufficientresistance to protect the circuit. According to another feature, thevoltage monitoring measurements are transmitted to the first integratedcircuit 402 through line 436.

According to one embodiment, when the voltage at the neutral line 438 ispositive with respect to line 406, it pulls up the center tap betweenthe first resistor 430 and the second resistor 432. Similarly, when thevoltage at the neutral line 438 is negative with respect to line 406, itpulls down the center tap between the first resistor 430 and the secondresistor 432. In one example, the voltage at the neutral line 438 ispositive 354 Volts. In another example, the voltage at the neutral line438 is negative 354 Volts with respect to line 406. According to onefeature, the second common node 434 is connected to a point betweenfourth 454 and fifth 456 Schottky diodes. In one example, the fourth 454and fifth 456 diodes act as protection diodes against voltage surges onthe AC line 406.

According to one aspect, a third integrated circuit 450 measures thecurrent on the line 406 through a current sensor 304. The thirdintegrated circuit 450 is coupled to the first integrated circuit 402and receives input from the first integrated circuit 402 through lines462 and 464. Lines 462 and 464 are high current outputs from the firstintegrated circuit 402. Lines 462 and 464 are paralleled at a fourthcommon node 466 and provide power to the integrated circuit 450.According to one feature, the output line 452 from the third integratedcircuit 450 to the first integrated circuit 402 carries a voltage ofabout 1.65 Volts. According to one example, the output voltage of 1.65Volts is about half scale. According to another feature, the output line452 from the third integrated circuit 450 to the first integratedcircuit 402 carries 15 mV/A. According to one feature, a zerocalibration and a gain calibration factor for the current sensor 304 arecalculated wirelessly during configuration of the current and voltagemonitoring circuitry 400, and stored as reference values.

According to one aspect, the transceiver in the first integrated circuit402 is coupled to antenna circuitry 410. The transceiver in the firstintegrated circuit 402 uses the antenna circuitry 410 to transmit thecurrent and voltage measurements. According to one embodiment, thetransceiver and the first integrated circuit 402 have a sleep current ofabout 1.4 μA and includes multiple accurate A/D channels.

According to another feature, the current and voltage monitoringcircuitry 400 includes a fourth integrated circuit 458. The integratedcircuit 458 is configured to allow a user to turn on the transceiver andcause the transceiver to pair with a master receiver. In one embodiment,when a magnet is placed in close proximity, the integrated circuit 458senses the magnet and causes the switch to close, turning on thetransceiver. The use of the magnet and switch provides a user interfacewithout a physical hole in the housing that could affect the integrityof the housing.

According to one feature, the power supply capacitor 308 stores energyfor the integrated circuit and transceiver 402 to use when it is awake.In some embodiments, the integrated circuit and transceiver 402 may drawa maximum amount of current from the main storage capacitor 418 at atime, and the power supply capacitor 308 may provide power needed by theintegrated circuit and transceiver 402 that exceeds the maximum amount.In one example, the maximum current the integrated circuit andtransceiver 402 may continuously draw from the main power storagecapacitor 418 is about 6.2 mA.

In one embodiment, the power supply capacitor 308 is a 47 μF capacitorand is charged to 14V. In one example, the power supply capacitor 308discharges linearly at a rate proportional to the current. According toone embodiment, the power supply capacitor 308 and the main powerstorage capacitor 418 form a capacitor divider that steps-down the ACvoltage for use in the power supply. According to one embodiment, thecurrent and voltage monitoring circuitry is configured to turn on forselected time periods without turning on the transceiver.

The current and voltage monitoring circuitry 400 includes a crystal 460,coupled to the first integrated circuit 402. The crystal 460 functionsto periodically wake up the integrated circuit 402. In one embodiment,the integrated circuit 402 is in a sleep mode the majority of the time.The crystal 460 wakes up the integrated circuit 402 for one line cycleand then the integrated circuit 402 returns to a sleep mode. In oneexample, the integrated circuit 402 samples the current and voltageusage measurements 32 times during one line cycle. In another example,the integrated circuit 402 samples the current and voltage usagemeasurements 20 times during one line cycle. In a further example, theintegrated circuit 402 samples the current and voltage usagemeasurements 16 times during one line cycle. In another example, theintegrated circuit 402 samples the current and voltage usagemeasurements 25 times over a 25 ms period, thereby taking one sample permillisecond.

According to one feature, the integrated circuit 402 wakes up, takessome samples, and then goes to sleep. A few cycles later, the integratedcircuit 402 wakes up again without turning on the transceiver andcompletes power calculations for the sample taken. The integratedcircuit 402 determines whether the calculations have changed frompreviously transmitted calculations by a predetermined, configurableamount and if so, prepares to transmit the calculations before going tosleep. A few cycles later, if determined necessary, the integratedcircuit 402 and the transceiver wake up and the transceiver transmitsthe calculations. In one embodiment, if the calculations have notchanged by more than a predetermined amount, then the transceiver doesnot transmit the calculations. According to one example, the integratedcircuit 402 wakes up once every five AC cycles to take measurements. Inother examples, the integrated circuit 402 wakes up to take measurementsonce every ten AC cycles, once every 20 AC cycles, once every 50 ACcycles, or once every 100 AC cycles.

According to one embodiment, the current sensor circuitry draws 9 mA.According to one feature, the current sensor is turned on asinfrequently as possible since it draws more current than the mainstorage capacitor 418 can continuously supply. In one example, thecurrent sensor has a 3.5 μs settling time and the ADC takes 132 μs for a12-bit reading. This is a 14% duty cycle, which equates to 1.26 mAaverage in addition to the 10 mA the processor draws. In anotherexample, the ADC takes 68 μs for a 10-bit reading.

FIG. 5 is a chart showing an exemplary sleep-wake cycle of an integratedcircuit and transceiver 402. Note that the chart 500 is not drawn toscale. The x-axis of the chart shows time and the y-axis shows currentusage. According to this example, over a five second period, theintegrated circuit and transceiver 402 is awake for 50 ms. During the 50ms the integrated circuit 402 is awake, it is measuring current andvoltage usage through the live line 406. During 40 ms of the 50 ms theintegrated circuit 402 is awake, it is consuming approximately 9 mA ofcurrent. During 10 ms of the 50 ms the integrated circuit 402 is awake,it is also transmitting the current and voltage usage measurements, andconsuming approximately 30 mA of current.

According to one feature, configuring the integrated circuit andtransceiver 402 to follow a sleep-wake cycle in which it is in a sleepmode the majority of the time, saves power, minimizing the size of thepower supply capacitor 308. According to one feature, minimizing thesize of the power supply capacitor 308 allows the current and voltagemonitoring circuitry 400 to physically fit inside the housing of thesocket 206 or the plug 202.

According to one example, the efficiency of a data center may becalculated using a power usage effectiveness (PUE) algorithm:

PUE=(total facility load)/(computing load)

where the total facility load is the total amount of power used by thedata center, including power for cooling, lighting and other overheadpower usage, and the computing load is the power used by the computingequipment. The PUE provides data center operators with an effectivemeasure of the efficiency of data centers, but determination of the PUEwith accuracy is often difficult. While determination of the total powerof the data center can be straightforward, it is often difficult todetermine how much of the total load is due to the computing equipmentin the data center. Embodiments of the invention can be used to measurepower usage by all computing equipment in a data center, resulting in amore accurate determination of the PUE.

FIG. 6 is a schematic diagram of a system 600 for monitoring the currentand voltage usage of multiple devices. The system 600 includes a cable602 having the current and voltage monitoring circuitry as well as atransceiver that uses a wireless low power communication standard, awireless receiver 604 that uses a wireless low power communicationstandard, for receiving the current and voltage usage levels transmittedfrom transceiver in the cable 602, and a computer 606 coupled to thewireless receiver 604. In one example, the wireless low powercommunication standard is IEEE standard 802.15.4. In another example,the wireless low power communication standard is a Zigbee® standard. Thecomputer 606 may monitor the current and voltage usage information fromthe cable, or a user may use the computer 606 to monitor the current andvoltage usage information. According to one embodiment, multiple cables602 are installed in a rack PDU and wirelessly transmit the current andvoltage levels via a transceiver that uses a wireless low powercommunication standard. According to one feature, the wireless receiver604 receives the current and voltage levels from multiple cables 602 andthe computer 606 monitors the current and voltage usage information fromthe cables 602.

FIG. 7 is a flow chart of a method 700 of monitoring the current andvoltage usage of multiple devices. At block 702, the plug end ofmultiple cables having current and voltage monitoring circuitry arecoupled to multiple power outlets in a rack. At block 704, the socketend of each cable is coupled to a computing unit. The current andvoltage monitoring circuitry in each cable measures current and voltageusage, and at block 706, a wireless transceiver in each cable transmitsthe measurements to a server via a wireless receiver. According to oneembodiment, voltage measurements are not taken during transmission bythe wireless transceiver, since the transmit current could affect thevoltage measurements. In one example, the wireless transceiver and thewireless receiver may use a wireless low power communication standard.In one example, the wireless low power communication standard is IEEEstandard 802.15.4. In another example, the wireless low powercommunication standard is a Zigbee® standard. At block 708, the currentand voltage usage information from each cable is monitored at theserver. In one example, the server automatically monitors the currentand voltage information. In another example, a user monitors the currentand voltage usage information collected at the server.

According to one embodiment, the systems and methods disclosed hereinare implemented in a three-phase power cord. In this embodiment, thecurrent and voltage monitoring circuitry includes three current sensingcircuits (one per phase) and three voltage detection circuits (one perphase), and one transceiver, one first integrated circuit, one powersupply capacitor 308 and one main storage capacitor 418. According toother embodiments, systems and methods disclosed herein may beimplemented in other multiphase power cords.

The systems and methods disclosed herein may provide an automated, easyto use, on location device for making measurements and calculations forthe user to maximize efficiency and increase system reliability.Embodiments may include a customer configurable set of variables and/orlimits to consider in performing the automated calculations in order toprovide customer the maximum flexibility in using the automated tools ina way that matches their desired level of safety. The systems andmethods may be used in conjunction with power monitoring software tofurther provide comprehensive checks of available power, considerhistoric and/or real-time (i.e., maximum and/or average loadinginformation) data, and consider power source losses in redundantsystems, as well as the user configurable maximum load thresholds toensure the user or operator configures attached loads for maximumrobustness and conformity to the user policy preferences to minimizeprobability of overload and dropped loads.

The embedded measurements, algorithms and calculations of data disclosedherein may be configured to provide recommendations for optimalconfiguration of power connections of attached equipment and otherrecommendations as described herein. Embodiments may include utilizingcommunication methods from external devices. Such external devices mayinclude other rack PDU's, other hardware (e.g., remote power panels orfeeder PDU's), and/or other external software, such as APC InfrastruxureCentral offered by American Power Conversion Corporation of WestKingston, R.I., or third party applications, and processing of this dataembedded into the rack PDU itself to provide user recommendations and/orcalculated data based on the external information and the data collectedwithin the rack PDU itself. Embodiments further include a display builtinto the rack PDU, such as LCD, LED, or other type of display, and anyassociated user interface which may be interactive to displaymeasurements or recommendations real time to a user at the rack PDU.Alternative embodiments may include an optional external displayconnected directly to the rack PDU, such as LCD, LED, or other type ofdisplay, and any associated user interface which may be interactive todisplay the measurements or recommendations real-time to a user at therack PDU. Methods to transmit this data to remote locations via anembedded web interface, SNMP, serial, or any other communication methodof the information processed in the rack PDU to other devices mayfurther be provided.

In certain embodiments, the measurements may be logged in an embeddedmemory of a network management card of the PDU, for example, for dataanalysis purposes. Operators may utilize the measurement data,particularly the current and power data, in order to achieve certainperformance improvements. For example, such measurement data may be usedto monitor the current draw to avoid circuit overloads. Another use formeasurement data may be to track power usage for capacity or coolingplanning.

In embodiments described above, power monitoring and transceivercircuitry is primarily described as being contained in a housing at asocket end of a power cord. In other embodiments, the circuitry may becontained in a housing at the plug end of a power cord or in housing atany point between the plug end and the socket end of a power cord.

Having thus described several aspects of at least one embodiment of thisinvention, it is to be appreciated various alterations, modifications,and improvements will readily occur to those skilled in the art. Suchalterations, modifications, and improvements are intended to be part ofthis disclosure, and are intended to be within the spirit and scope ofthe invention. For example, alternative configurations of electricalcomponents may be utilized to produce similar functionality, forexample, transceiver functions, or other functions. Accordingly, theforegoing description and drawings are by way of example only.

What is claimed is:
 1. A cable, comprising: a plug at a first end of thecable; a socket at a second end of the cable; first and secondconductors extending from the plug to the socket; a current and voltagemonitoring module coupled to the first and the second conductors andconfigured to measure current and voltage levels of the conductors; atransceiver coupled to the current and voltage monitoring module,configured to receive data related to the current and voltage levels andtransmit the data related to the current and voltage levels; and ahousing configured to house the current and voltage monitoring module,the transceiver, and one of the socket and the plug.
 2. The cable ofclaim 1, wherein the transceiver is configured to use a wireless lowpower communication protocol to transmit the data related to the currentand voltage levels.
 3. The cable of claim 2, wherein the wireless lowpower communication protocol is IEEE standard 802.15.4.
 4. The cable ofclaim 1, wherein the current and voltage monitoring module is configuredto operate in one of a sleep mode and a wake mode.
 5. The cable of claim1, further comprising a capacitor configured to store operating powerfor at least one of the current and voltage monitoring module and thetransceiver.
 6. The cable of claim 5, wherein the current and voltagemonitoring module is configured to charge the capacitor in a sleep modeof operation.
 7. The cable of claim 1, wherein the socket is a IEC C13standard socket.
 8. The cable of claim 1, wherein the plug is a IEC C14standard plug.
 9. The cable of claim 1, wherein the cable is a threephase cable. 10-20. (canceled)